Riser sections and methods for making same

ABSTRACT

A riser section for joining to another riser section to form a drilling riser includes a weld region generated by welding a first riser tube to a second riser tube. The weld region includes a fusion zone in which material of the first riser tube coalesces with material of the second riser tube, and a heat-affected zone adjacent the fusion zone. The riser section also includes a cover positioned over the weld region and welded to the first riser tube and to the second riser tube such that the cover covers the fusion zone and the heat-affected zone to protect the zones. The cover may be a solid piece of material that is welded to the riser tubes, or the cover may be a bead of weld filler material that is welded (melted and deposited) onto the weld region of each of the riser tubes.

CROSS REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY

This application claims priority from commonly owned U.S. Provisional Patent Application 61/548,850 filed 19 Oct. 2011, and titled “Aluminum Pipe with a Surface Coating Welded to a Heat Affected Zone to Cover the Exposed Surface and Mitigate Corrosion, and Methods for Making the Same”, presently pending, which is incorporated by reference.

BACKGROUND

Risers are vital to drilling and extracting oil and other materials from below the earth's surface. A riser is basically a tube that connects a well head to a control station where extraction, and, frequently, drilling operations are controlled. When extracting oil, natural gas and/or other materials from underneath the bottom of a body of water, such as a sea, ocean or lake, a riser connects the wellhead at the bottom of the body of water to a platform suspended at the water's surface. In such systems, the riser protects the drill string that extends from the platform and through the wellhead, by encasing the drill string between the platform and wellhead. The riser also provides a conduit for drilling-mud to flow from the platform to the wellhead, and thus into the well. Drilling-mud helps control the pressure inside the well that would otherwise substantially drop because of the hole drilled into the earth. The riser also provides a conduit for the oil, natural gas, and/or other materials to flow from the wellhead to the platform where the oil, natural gas and/or other materials can be secured for subsequent use.

Most risers include a main line and one or more auxiliary lines. The main line encases the drill string as it extends from the platform to the wellhead, and contains the drilling-mud and/or oil and/or other materials as they flow to and from the wellhead and the control station. The one or more auxiliary lines are typically located adjacent and outside of the main tube, and encase control lines that extend from the platform to the wellhead. The control lines may be hydraulic lines, electrical and/or pneumatic lines that connect systems at the wellhead, such as a blowout preventer (BOP) that can cap the well in an emergency.

Most risers are assembled in the field by coupling riser sections together. For example, FIG. 1 shows a portion 10 of a riser that includes six riser sections 12 coupled end-to-end. Each section 12 includes two main tubes 14 coupled end to end, and two flanges 16, each coupled to a respective one of the main tubes 14. Each of the flanges 16 are designed to be mounted to a flange of another section 12 by bolts to form the portion 10 of the riser.

Because the distance between the control center and the wellhead is often long—especially when the wellhead is located at the bottom of a sea, ocean or lake —most risers include hundreds of riser sections coupled end to end. To reduce the number of sections to be connected to each other via their flanged ends, riser sections 12 are typically formed by welding two or more of the main tubes 14 (which are typically about 30 feet long each) together, end to end, and then welding the flanges 16 to the remaining two ends of the section 12. If the riser tubes 14 are made of a metal, such as aluminum, whose crystalline structure and/or alloy distribution is altered by the heat generated from the welding process, then welding such tubes can generate a weld region (an example is shown in FIG. 3) that includes the altered crystalline structure and/or altered alloy distribution. Such weld regions typically include a fusion zone in which the material from the two tubes coalesce and a heat-affected zone adjacent the fusion zone. Such weld regions are less resistant to damage from bumps and/or abrasion, which often occur when the drill string rotates within the riser. Such weld regions are also less resistant to surface corrosion than the main tube's material outside the heat-affected zone.

To correct the crystalline structure and/or alloy distribution in the weld regions one can heat treat the weld region. Unfortunately, though, such corrective heat treatment does not eliminate the susceptibility to corrosion of the fusion zone and the heat-affected zone. Thus, a surface coating is often applied to the weld region of a riser section. Unfortunately, though, such surface coatings are often chipped or worn away by the frequent bumps of the drill string against the weld region, thus leaving the inside surface of a weld region exposed. And similarly, such surface treatments are often dissolved or removed by the harsh, deep-sea environment, thus leaving the outside surface of a weld region exposed.

SUMMARY

In an aspect of the invention, a riser section for joining to another riser section to form a drilling riser, includes a weld region generated by welding a first riser tube to a second riser tube. The weld region includes a fusion zone in which material of the first riser tube coalesces with material of the second riser tube, and a heat-affected zone adjacent the fusion zone. The riser section also includes a cover positioned over the weld region and welded to the first riser tube and to the second riser tube such that the cover covers the fusion zone and the heat-affected zone to protect the zones. The cover may be a solid piece of material that is welded to the riser tubes, or the cover may be a bead of weld filler material that is welded (melted and deposited) onto the weld region of each of the riser tubes.

By covering the weld region's fusion zone and heat-affected zone, the cover protects a surface of the weld region that is susceptible to corrosion. When the cover is welded to an exterior surface of the riser section, then the cover protects the weld region from the harsh, deep-sea environment. When the cover is welded to an interior surface of the riser section, then the cover protects the weld region from bumps and abrasions caused by the drill string moving inside the riser section, and from drilling-mud and other materials as they flow through the riser section.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view of a portion of a conventional riser.

FIG. 2 is a perspective view of a section of a riser, according to an embodiment of the invention.

FIG. 3 is a partial, cross-sectional view of the riser section shown in FIG. 2, according to an embodiment of the invention.

FIG. 4 is a partial, cross-sectional view a riser section, according to another embodiment of the invention.

FIG. 5 is a partial, cross-sectional view of a riser section 90, according to yet another embodiment of the invention.

DETAILED DESCRIPTION

FIG. 2 is a perspective view of a section 30 of a riser, according to an embodiment of the invention. The riser section 30 includes two flanges 32 that may be coupled (here with a nut threaded onto a bolt inserted through a hole 33) to flanges (not shown) of other riser sections (also not shown) to form a drilling riser (not shown but similar to the riser shown in FIG. 1). The drilling riser may encase a drill string 34 extending from a drilling platform (not shown) into a well (also not shown) to protect the drill string 34 as the drill string moves (rotates and/or translates) relative to the well. The drilling riser may also provide a conduit for drilling-mud (not shown) to flow to and from the drilling platform and well.

The riser section 30 includes a plurality of riser tubes 36 (here two) that are welded together at their respective ends 38, two flanges 32 each welded to a respective one of the riser tube's other ends 40, and a cover 42 that protects a weld region 44. In this and other embodiments, the riser section 30 includes three covers 42 (a portion of each not shown for clarity) each protecting a respective one of three weld regions 44—the weld region 44 between the two riser tubes 36, and the weld regions 44 between the riser tubes 36 and the flanges 32. The cover 42 may be a solid piece of material that is welded to the riser tubes 36, or the cover 42 may be a bead of weld filler material that is welded (melted and deposited) onto the weld region of each of the riser tubes 36.

As a result of the welding operations, each of the weld regions 44 includes a fusion zone 46 (shown in FIGS. 3-5) in which the material from the two tubes coalesce, and a heat-affected zone 48 (also shown in FIGS. 3-5) adjacent the fusion zone 46. The material in each of these zones includes a crystallinity and/or alloy distribution that has been adversely modified by the heat generated during the welding process, and thus an exposed surface of the weld region 44 is more susceptible to corrosion. By covering an exposed surface of the fusion zone 46 and the heat-affected zone 48 of a weld region 44, the cover 42 helps isolate the surface of the weld region 44 from its surrounding environment, and thus helps prevent the environment from corroding and otherwise damaging the weld region 44. When the cover 42 is welded to an exterior surface of the riser section 30 (as shown in FIGS. 2, 3 and 5, and discussed in greater detail in conjunction with FIG. 3), then the cover 42 protects the weld region 44 from the harsh, deep-sea environment. When the cover 42 is welded to an interior surface of the riser section 30 (as shown in FIGS. 4 and 5, and discussed in greater detail in conjunction with FIG. 4), then the cover protects the weld region 44 from bumps and abrasions caused by the drill string moving inside the riser section 30, and from drilling-mud and other materials as they flow through the riser section 30.

Although the riser section 30 is formed from two riser tubes 36 in this and other embodiments, the riser section 30 may also be formed by welding three or more riser tubes 36 together. Furthermore, in other embodiments one or both of the flanges 32 may be coupled to their respective riser tubes 36 by any fastening means other than welding, and the means for coupling two flanges together to join two riser sections together may include any desired fastening means other than a nut threaded onto a bolt. In still other embodiments, the riser tubes 36 may be joined together by any means other than welding, and one or both of the flanges 32 may be welded to their respective riser tubes 36.

FIG. 3 is a partial, cross-sectional view of the riser section 30 shown in FIG. 2, according to an embodiment of the invention. In this embodiment the cover 42 is welded to an exterior surface of the riser section 30. More specifically, the cover 42 is welded to an exterior surface of the first riser tube 36 a and to an exterior surface of the second riser tube 36 b. In this embodiment, the riser section 30 also includes a relief zone 50 that reduces the ability of the drill string 34 to bump and abrade the fusion zone 46 and the heat-affected zone 48 of the weld region 44.

The cover 42 may be sized and shaped as desired to protect the weld region 44. For example, in this and other embodiments, the cover 42 extends across the whole weld region 44 and has a thickness of about 0.1 inches. In addition, the shape of the cover 42 mimics the contour of the outside surfaces of the riser tubes 36 a and 36 b. More specifically, the cover 42 is cylindrical and surrounds the weld region 44 that exists in the circumference of the riser section ends 38 a and 38 b. In other embodiments, the cover 42 may be thicker or thinner than 0.1 inches, and may only cover a portion of the weld region 44.

The cover 42 may include any desired material capable of protecting the weld region 44 in a harsh, deep-sea environment. For example, in this and other embodiments, the cover 42 includes material identical to the material of the riser tubes 36 a and 36 b to minimize galvanic corrosion. The material of the riser tubes 36 a and 36 b may be any desired material that will provide adequate strength and/or toughness to handle the stress and strain in the riser section 30 that is applied during service. In this and other embodiments, each of the tubes 36 a and 36 b is made of aluminum designated as Russian Alloy 1953-T1 or 1980-T1. This aluminum has a great strength to weight ratio which can be very important in offshore drilling because the weight of the riser suspended in the water must borne by either the drilling platform or ship, or the well head underneath the water. Thus, in this and other embodiments, the cover 42 is also made of aluminum designated as Russian Alloy 1953-T1 or 1980-T1. In other embodiments, the tubes' material may be other aluminum alloys, such as 7050-T7 or 7075-T6, and thus the cover 42 may be made of 7050-T7 or 7075-T6 aluminum alloy. In still other embodiments, the tubes' material may be any desired iron alloy, and thus the cover 42 may be any desired iron alloy.

Still referring to FIG. 3, the cover 42 may be welded to the riser tubes using any desired welding technique capable of holding the cover 42 to the exterior surfaces of the riser tubes 36 a and 36 b while the riser section is exposed to the harsh, deep-sea environment. For example, in this and other embodiments, the cover 42 is lap welded to the riser section to cover the weld region 44. In other embodiments, the cover 42 may be welded to the riser section by gas-tungsten-arc welding, by gas-metal-arc welding, by laser welding, or any variation thereof. In still other embodiments, gas-tungsten-arc and/or gas-metal-arc welding may be used to simply apply a bead of weld filler material to the weld region 44 to cover the region 44.

Other embodiments are possible. For example, the cover 42 may be sized to cover only a portion of the weld region 44. The cover 42 may also be thicker or thinner than 0.1 inches, and may be mounted to the riser section 30 using any other desired means, such as using an adhesive to mount the cover 42 to the riser section 30. In addition, the weld region 44 and/or the cover 42 may include a surface coating (not shown) applied to the surface of the weld region 44 and/or the surface of the cover 42 to help protect the weld region 44. The surface coating may be any desired coating that provides the desired protection. For example, the surface coating may include a marine, two-part epoxy paint, thermal-sprayed commercially-pure aluminum, thermal-sprayed zinc containing aluminum, oil-based paint, and/or water based paint.

Still referring to FIG. 3, the riser section 30 also includes a relief zone 50 that reduces the ability of the drill string 34 to bump and abrade the weld region 44 by spanning an interior surface 52 of the riser section 30 where the fusion zone 46 and the heat-affected zone 48 are located. As the drill string 34 moves within the riser section 30, the drill string bumps and abrades the weld regions 44. Because the crystallinity and/or alloy distribution of the riser tube's material is altered in the weld regions 44, the bumps and abrasions exerted on the weld region 44 can damage the riser tubes 36 a and 36 b. The relief zone 50 helps protect a weld region 44 from damage by reducing or eliminating the drill string's ability to contact the weld region 44 as the drill string moves within the riser section 30. Thus, the potential for damage to the riser section 30 that can result from bumping and/or abrading a portion of the riser tube's material that suffers an adverse change in its crystallinity and/or alloy distribution can be mitigated.

The relief zone 50 is located where the two tubes 36 a and 36 b are welded together. And although FIG. 3 shows the relief zone 50 located here, in this and other embodiments other relief zones 50 may be located anywhere two or more components of the riser section 30 are welded together such that the resulting weld region 44 is exposed to the drill string 34 and/or exposed to other components of a drilling/or mineral extraction operation that could bump and/or abrade the weld region 44. Therefore, the discussion of the relief zone 50 shown in FIGS. 3-5 may also apply to relief zones 50 located elsewhere in the riser section 30, such as the relief zones 50 where each of the flanges 32 (FIG. 2) are welded to a respective one of the riser tubes 36 a and 36 b.

The two riser tubes 36 a and 36 b may be welded together using any desired welding technique. For example, in this and other embodiments the riser tubes 36 a and 36 b are friction stir welded together using a technique similar to the technique discussed in U.S. Pat. No. 5,813,592 titled FRICTION STIR WELDING, issued 29 Sep. 1998 to Midling et al. Specifically, each riser tube 36 a and 36 b includes a respective one of the ends 38 a and 38 b, and each of the ends are held adjacent each other as a cylinder-shaped tool (not shown) that is harder than the material of the riser tubes 36 a and 36 b is pressed against the outside surfaces 54 a and 54 b of the riser tubes 36 a and 36 b and spun against the surfaces. As the tool spins, the friction between the outside surfaces 54 a and 54 b and the tool heats the material in the ends 38 a and 38 b. By controlling the rotational speed of the tool, and the pressure and friction between the outside surfaces 54 a and 54 b and the tool, one can control the amount of heat generated by the tool spinning against the outside surfaces 54 a and 54 b. With enough heat the ends 38 a and 38 b plastically deform and allow the material in these regions to coalesce with each other to join the riser tubes 36 a and 36 b. In this and other embodiments, the riser section 30 includes a longitudinal axis 56.

Still referring to FIG. 3, the relief zone 50 includes an interior surface 60 that extends over the weld region 44 and is located a distance 62 from the longitudinal axis 56 that is longer than the distances 64 a and 64 b to the second interior surface 52 that is adjacent the relief zone 50. The difference between the distance 62 and the distances 64 a and 64 b may be any desired length that sufficiently offsets the interior surface 60 from the drill string 34 as the drill string moves inside the riser section. For example in this and other embodiments, the difference in length between the two distances 62 and 64 a is 0.090 inches, and the difference in length between the two distances 62 and 64 b is also 0.090 inches. The distance 64 to the second interior surface 52 is measured perpendicular to the longitudinal axis 56, and in this and other embodiments is nineteen inches. The distance 62 to the interior surface 60 of the riser tube 36 b is also measured perpendicular to the longitudinal axis 56, and in this and other embodiments is 19.090 inches.

By offsetting the interior surface 60 of the relief zone 50 0.090 inches from the second interior surfaces 52, the interior surface 60 remains apart from the drill string 34 as the drill string moves inside the riser section 30 (FIG. 2). Consequently, the drill string 34 does not bump and/or abrade the inside surface of the weld region 44, which helps prevent damage to the riser section 30.

In this and other embodiments, the relief zone 50 extends over the whole area of the weld region 44 that is exposed to the interior of the riser section 30, that is, that faces the longitudinal axis 56. Specifically, the relief zone 50 extends three inches along the direction of the longitudinal axis 56, and follows the interior periphery of the riser section 30 where the two ends 38 a and 38 b are welded together. Furthermore, the difference between the distances 62 and 64 (the offset for the relief zone's interior surface 60) is the same or substantially the same throughout the whole area of the relief zone's interior surface 60. Thus, the relief zone 50 is cylindrically shaped and surrounds a portion of the longitudinal axis 56.

Other embodiments are possible. For example, the distances 64 a and 64 b may be different while the difference between the distances 62 and 64 a, and 62 and 64 b may remain the same, or be different. As another example, the relief zone 50 may extend over a portion of the weld region 44. This may be desirable when the portion of the weld region 44 that the relief zone does not cover is not likely to be bumped or abraded by the drill string 34, and/or when the affect of the relief zone 50 on the flow of drilling-mud, oil, or other fluids within the riser section 30 is worse than the risk of damage to the weld region 44 of the section 30 from the drill string 34.

Still referring to FIG. 3, the relief zone 50 may also include a transition region 68 disposed between the interior surface 60 of the relief zone 50 and the second interior surface 52 to reduce the stress concentration that occurs when the wall of the riser section changes in thickness. Because the riser section 30 carries much of the weight of all the riser sections below it in the drilling riser, and resists the crushing load of the water and/or earth that surrounds it, the riser section 30 experiences much stress. To reduce the concentration of the stress that occurs from a sudden change in the amount of material carrying the loads, the transition region 68 reduces the rate at which the thickness changes from the interior surface 60 to the second interior surface 52. In this and other embodiments, the transition region includes a fillet radius 70 whose length is 0.090 inches. In other embodiments, the fillet radius may be shorter or longer than 0.090 inches. In still other embodiments, the transition region 68 may be any desired contour, such as a straight ramp.

Still referring to FIG. 3, the riser section 30 may include a surface coating (not shown) applied to the interior surface 60 and transition region 68 of the relief zone 50 to help protect the weld region 44. The surface coating may be any desired coating that provides the desired protection. For example, in this and other embodiments, the surface coating includes a marine, two-part epoxy paint. In other embodiments, the surface coating may include thermal-sprayed, commercially-pure aluminum, thermal-sprayed zinc containing aluminum, oil-based paint, water based paint, and/or any desired conversion coating.

FIG. 4 is a partial, cross-sectional view of a riser section 80, according to another embodiment of the invention. The riser section 80 is similar to the riser section 30 shown in FIGS. 2 and 3 except a cover 82 is welded to the interior surface 84 of the riser section 80, and the exterior surface of the riser section 80 does not include a cover 82 covering the weld region 86. Likewise, the cover 82 is similar to the cover 42. This configuration may be desirable when the riser section is used in an environment that is not as harsh as a deep-sea environment, such as a shallow freshwater environment. In other embodiments, the interior surface 84 may not be located in a relief zone, and thus the cover 82 may be located outside a relief zone.

FIG. 5 is a partial, cross-sectional view of a riser section 90, according to yet another embodiment of the invention. the riser section 90 is similar to the riser section 30 shown in FIGS. 2 and 3 except a first cover 92 is welded to the exterior surface 94 of the riser section 90, and a second cover 96 is welded to the interior surface 98 of the riser section 90. Likewise, the covers 92 and 96 are similar to the cover 42 and cover the weld region 98. This configuration may be desirable when the riser section is used in a harsh, deep-sea environment and the drilling mud 

What is claimed is:
 1. A riser section for joining to another riser section to form a drilling riser, the riser section comprising: a weld region generated by welding a first riser tube to a second riser tube, the weld region including: a fusion zone in which material of the first riser tube coalesces with material of the second riser tube, and a heat-affected zone adjacent the fusion zone; and a cover positioned over the weld region and welded to the first riser tube and to the second riser tube such that the cover covers the fusion zone and the heat-affected zone to protect the zones.
 2. The riser section of claim 1 wherein the cover is weld filler material that is melted and deposited onto the fusion zone and the heat-affected zone.
 3. The riser section of claim 1 wherein the first riser tube and the second riser tube, each includes an exterior surface, and the cover is welded to the exterior surface of the first riser tube and to the exterior surface of the second riser tube.
 4. The riser section of claim 1 wherein the first riser tube and the second riser tube, each includes an interior surface, and the cover is welded to the interior surface of the first riser tube and to the interior surface of the second riser tube.
 5. The riser section of claim 1 wherein the weld region is generated by friction stir welding the first riser tube to the second riser tube.
 6. The riser section of claim 1 further comprising: a longitudinal axis; and a relief zone that spans both the fusion zone and the heat-affected zone, the relief zone having an interior surface disposed a distance away from the longitudinal axis in a direction perpendicular to the axis that is greater than the distance of a second interior surface adjacent the relief zone's interior surface from the longitudinal axis in a direction perpendicular to the axis.
 7. The riser section of claim 1 further comprising: a longitudinal axis; a relief zone that spans both the fusion zone and the heat-affected zone, the relief zone having an interior surface disposed a distance away from the longitudinal axis in a direction perpendicular to the axis that is greater than the distance of a second interior surface adjacent the relief zone's interior surface from the longitudinal axis in a direction perpendicular to the axis; and a second cover positioned over the weld region in the relief zone and welded to the first riser tube and to the second riser tube such that the second cover covers the fusion zone and the heat-affected zone to protect the zones.
 8. The riser section of claim 1 wherein the first riser tube includes a material, and the second riser tube and the cover, each includes material that is the same as the first riser tube's material.
 9. The riser section of claim 1 wherein the cover includes an aluminum alloy.
 10. The riser section of claim 1 wherein the cover includes an iron alloy.
 11. The riser section of claim 1 wherein the shape of the cover mimics the contour of the weld region.
 12. The riser section of claim 1 wherein the cover has a thickness that is 0.1 inches.
 13. A method for forming a riser section that may be coupled with other riser sections to form a drilling riser, the method comprising: welding a first riser tube to a second riser tube; positioning a cover over a weld region generated by welding the first riser tube to the second riser tube, such that the cover covers the fusion zone of the weld region and the heat-affected zone of the weld region; and welding the cover to the first riser tube and to the second riser tube.
 14. The method of claim 13 wherein welding the first riser tube to the second riser tube includes friction stir welding.
 15. The method of claim 13 wherein welding the cover to the first riser tube and to the second riser tube includes gas tungsten arc welding.
 16. The method of claim 13 wherein: positioning the cover over the weld region includes positioning the cover over an exterior surface of the first riser tube and over an exterior surface of the second riser tube, welding the cover to the first riser tube includes welding the cover to the exterior surface of the first riser tube, and welding the cover to the second riser tube includes welding the cover to the exterior surface of the second riser tube.
 17. The method of claim 13 wherein: positioning the cover over the weld region includes positioning the cover over an interior surface of the first riser tube and over an interior surface of the second riser tube, welding the cover to the first riser tube includes welding the cover to the interior surface of the first riser tube, and welding the cover to the second riser tube includes welding the cover to the interior surface of the second riser tube.
 18. The method of claim 13: wherein: welding the cover to the first riser tube includes welding the cover to an exterior surface of the first riser tube, and welding the cover to the second riser tube includes welding the cover to an exterior surface of the second riser tube; and further comprising: positioning a second cover over the weld region, an interior surface of the first riser tube, and an interior surface of the second riser tube, such that the second cover covers the fusion zone and the heat-affected zone of the weld region, welding the second cover to the interior surface of the first riser tube, and welding the second cover to the interior surface of the second riser tube.
 19. The method of claim 13 further comprising forming a relief zone that spans the fusion zone and the heat-affected zone of the weld region.
 20. The method of claim 13 further comprising: forming a relief zone that spans the fusion zone and the heat-affected zone of the weld region, positioning a second cover over the weld region in the relief zone, welding the second cover to an interior surface of the first riser tube, and welding the second cover to an interior surface of the second riser tube.
 21. The method of claim 13 wherein positioning and welding the cover includes melting weld filler material and depositing the molten filler material onto the fusion zone and the heat-affected zone. 